It is a lying exercise. With dumbells you will extend your arms from in front of your chest to behind your head (back and forth) like a Dumbbell Pullover, but rather in this situation you will have Dumbbells in each of your hands, and instead of the combination of the dumbbells and your wrist being perpendicular to the floor, it is parallel.

Does anyone know the name of this exercise, if it works, and what muscle group it has the potential of exercising?